The present invention relates to electrically powered liquid heating vessels, such as kettles or hot water jugs incorporating heating elements, and in particular to an adaptor which will allow such vessels to be powered from a domestic electric cooking apparatus.
Electrically powered water heating vessels such as kettles and hot water jugs are widely used in countries such as the United Kingdom and Australia, for heating water in quantities of say up to 2 liters, sufficient for making tea, coffee and other hot beverages, in the home. Typically such vessels incorporate an immersion heating element rated at around 2000-2500 W, which allows water to be boiled quickly. This is possible because the mains voltage available from wall sockets, from which such vessels are powered, is nominally 220/240 V and therefore a current of the order of 10 A is typically drawn by the element which is acceptable for such an appliance.
Power may be supplied to the vessel in one of two ways. In the most traditional arrangement an electrical power lead has a plug connector at one end, for engagement with the wall socket, and at the other end a socket connector for direct engagement with terminal pins extending from the vessel, which is free standing. In a more recently introduced and increasingly popular arrangement, the vessel is provided with a separate base unit, upon which it normally rests. An electrical power lead again has a plug connector for engagement with the wall socket, but is fixedly connected at its other end to a socket connector mounted within the base unit with which the terminal pins of the vessel engage automatically when the vessel is placed upon the base unit to supply power to the heating element of the vessel. Thus, when it is desired in the latter type of device to pour liquid from the vessel, it is merely lifted from the base unit, so automatically disconnecting the power from the vessel.
This so called "cordless" arrangement is convenient since it is no longer necessary to unplug the lead from the vessel every time liquid is to be poured from it. An example of such a construction is described in commonly owned U.S. Pat. No. 4,934,955, the disclosure of which is incorporated herein by reference.
These vessels nowadays nearly all have built in switch means which allow them to be manually turned on and off, and which are also openable in response to liquid in the vessel boiling, so as automatically to disable the heater when the liquid boils. A protector switch means is also traditionally provided for disabling the heater in the event of it overheating e.g. after having been switched on with insufficient liquid in the vessel to cover the element.
In the United States, however, domestic wiring regulations are different from those in countries such as the United Kingdom. A transformer placed in the domestic supply provides a 220 V, split phase, supply. Wall sockets are connected across a half phase, which means that they effectively receive only a 110 V supply. Thus while electric kettles are known in the United States, they have to be lower wattage devices, typically 1600 W in order to keep the current within acceptable limits. This means that they take a relatively long time to boil water and for this reason, kettles are not popular in the United States. It is more common to boil water in saucepans on cookers which is both time consuming and inconvenient. There is no immersion heater, and no automatic cut-out switching is available.
In the United States domestic cookers are traditionally hard wired into the power supply across the full 220 V supply, so that cooker heating elements can be run at higher wattages than appliances from standard wall sockets.
Moreover, it is standard in U.S. domestic cookers for the hob heating elements to be removable, so that the wells underneath the elements can easily be cleaned. Thus, typically, a heating element is provided with push fit terminals which engage with a socket, or receptacle, provided in the side wall of the element well.